Endfire array having vertically and horizontally spaced parasitic arrays



6, 1965 H. w. EHRENSPECK 3, 5

'ENDFIRE ARRAY HAVING VERTICALLY AND HORIZONTALLY .SPACED PARASITIC ARRAYS Original Filed March 6, 1958 3 Sheets-Sheet. 1

INVENTOR fl'i/VA/V/V 4447/ #52564 Nov. 16, 1965 H. w. EHRENSPECK 3,

ENDFIRE ARRAY HAVING VERTICALLY AND HORIZONTALLY SPACED PARASITIC ARRAYS Original Filed March 6, 1958 3 Sheets-Sheet 2 Z0 0 o o o o 0 k 0 o o o o o o o e o M 6 /Z-- o o o o o o o o IQ go o o o o o o o o o o o o o o /7 M ,0 o o 0 o o o o 0 A9 A8 /J o o o o o o o o o 0 0 o o o 0 j INVENTOR. Awe MAW M EVIIA/I/ZCK Nov. 16, 1965 H. w. EHRENSPECK 3,2 3,

ENDFIRE ARRAY HAVING VERTICALLY AND HORIZONTALLY SPACED PARASITIC ARRAYS Original Filed March 6, 1958 3 Sheets-Sheet 3 ENDFETRE ARRAY HAVTNG VERTIQALLY AND HGRZZQNTALLY SPACED PARASTTIC ARRAYS Hermann W. Ehrenspecir, 94 Farnham St., Belmont, Mass. Griginal application Mar. 6, 1958, Ser. No. 719,d98, now Patent No. 3,ii96,520, dated .luiy 2., 1963. Divided and this application June 25, 1963, Ser. No. 290,569

4 Claims. (Cl. 343819) (Granted under Title 35, US. Code (1952), sec. 266) The invention described herein may be manufactured and used by or for the United States Government for governmental purposes without payment to me of any royalty thereon.

This application is a division of my application, Serial No. 719,698, filed March 6, 1958, now Patent No. 3,096,520.

This invention relates generally to antennas, and more particularly to a method and means for controlling the amplitude and phase across a virtual aperture.

Endfire arrays, such as Yagi antennas, may be analyzed in terms of the amplitude and phase distribution in a virtual aperture plane transverse to the array axis and located at the end of the array. Arrays of this type usually have high side lobes like horns which, according to this invention, may be reduced by affecting the amplitude and phase distribution in the virtual aperture of the endfire array.

According to the teachings of my invention, both amplitude and phase distribution may be affected by placing one or more parasitic side rows on both sides of the center array, thus transforming the array into a twodimensional array.

The utilization of the parasitic arrays of my invention provide a reduction in side lobes, increased gain, and increased bandwidth with respect to pattern.

It is, therefore, an object of my invention to produce a novel method and means for reducing side lobes of an antenna pattern.

It is another object of my invention to produce a novel endfire array having good side lobe reduction and increased gain.

It is still another object of my invention to produce a novel method and means for increasing antenna bandwidth with respect to pattern.

It is a further object of my invention to provide a novel method and means for producing side lobe reduction which may be applied to existing endfire arrays.

It is a still further object of my invention to produce a novel means for side lobe suppression not requiring additional feed systems.

Another object of my invention involves the utilization of parasitic side rows to a center array in the vertical as well as horizontal direction to improve pattern and gain performance.

Still another object of my invention involves the utilization of a novel means for side lobe reduction applicable to both high and low frequency antennas.

A further object of my invention involves the production of an antenna suitable for use for scatter propagation.

These and other advantages, features and objects of the invention will become more apparent from the following description taken in connection with the illustrative embodiments in the accompany drawings, wherein:

FIG. 1 is a representation of an antenna array with two parasitic side rows;

FIG. 2 is a plan view of a two-dimensional endfire array with six parasitic side rows;

FIG. 3 is a schematic end view of a three-dimensional endfire array illustrating the relative positions of the main 3,218,645 Patented Nov. 16, 1965 array and the parasitic arrays; FIGURE 3a is an isometric view of FIGURE 3; and

FIG. 4 is a schematic representation of an arrangement for rendering the parasitic arrays suitable for scatter propagation.

The end of an array may be considered to be a radiating aperture, and because there are no physical limits, it is called a virtual aperture. Since power levels more than approximately 20 db below maximum do not make substantial contribution to the far field pattern of an array, the virtual aperture of an endfire array may be expressed in terms of wavelength as is done with broadside arrays; therefore, the gain and pattern of an endfire array may be expressed as a function of the amplitude distribution and phase distribution in the virtual aperture. Accordingly, changes in both gain and pattern may be accomplished by changing the width of the virtual aperture and the amplitude and phase distribution Within said aperture. An array change from single to two-dimensional allows an increase in gain by increasing the virtual aperture; reducing side lobes by changing amplitude and phase distribution within said aperture; and simultaneously increasing gain and achieving side lobe reduction by changing both aperture distribution and width.

Referring to FIG. 1, a ground plane 10 may be used, although it does not form a necessary part of my invention. Mounted on the ground plane it is an example of an endfire antenna shown as a Yagi array 11 of monopoles with a reflector 12. A coaxial feed means 13 excites the array from beneath the ground plane.

It was found that the width of, and distribution in the virtual aperture at effective energy levels can be changed in the desired manner by symmetrically placing one or more shorter rows of parasitic elements 14- and 15 on either side of the center array. The utilization of a nonsymmetrical arrangement produces a change in pattern. Parasitic side rows 14 and 15 act as smaller wave channels fed mainly by coupling from the main center array 11 which results in a two-dimensional parasitic endfire array excited by a single feed 13 of the main array 11.

The dotted line portion represents an aperture plane with arbitrary limits of 20 db of maximum power level in the vertical and transverse directions.

Side rows 14 and 15 are adjusted so that the phase front in the virtual aperture is as uniform as possible and the amplitude distribution is given the form needed for a specified pattern. Phase may be controlled by adjusting the phase velocity which depends on the spacing, height, and diameter of the parasitic elements. An infinite number of combinations of these parameters may be used to achieve a desired phase velocity. Amplitude may be controlled by variation of side row length. The adjustments of the phase front and amplitude distribution can be performed, within limitations, relatively independently of each other.

In order to couple sufficient energy to the side arrays 14 and 15, the usual placement of these arrays falls within the virtual aperture. The phase deviation in the virtual aperture of the center array 11 without the parasitic side rows undulates and side row displacement is usually made at the point of maximum deviation; however, adjustment of the various parameters allows a placement anywhere within the virtual aperture and even slightly outside it depending on the amount of coupling energy desired.

Tests made on the array of FIG. 1 indicate an increased gain of 30% and an increased virtual aperture of 37% using the following exemplary physical dimensions:

Length of center array 11 6.0x Length of parasitic side rows 14 and 15 3.2x Side row spacing from center array .66A

3 Element spacing v .20)\ Element diameter .048A

FIG. 2 is a top view of an antenna having a center array 11 with reflectors 12, a feed 13 and six side rows 16, 17, 18, 19, and 21 wherein the virtual aperture is increased by 66% above the Yagi type endfire array, and the measured gain increase is 60%.

An extension of the principle of this .invention to increase the height of the virtual aperture in the vertical direction would be to place side arrays above (and below if there is no ground plane) the center array 11. By thus passing from a two-dimensional to a three-dimensi-onal array a further increase in gain results. FIG. 3 is a schematic representation of an end view of a three-dimensional antenna having a central Yagi array 11 and parasitic arrays 22, 23, 24 and 25. Of course the absence of a ground plane indicates the use of dipoles rather than monopoles in this embodiment. Since the parasitic arrays do not act as reflectors, the height of the elements of the arrays will be less than a quarter wavelength for monopol s and a half wavelength when dipole elements are used. As shown in FIG. 3a, which is an isometric view of the embodiment of FIG. 3, the parasitic arrays 22, 24, 23 and 25 are spaced from the main array 11. Thus, the resultant antenna appears to be similar to the embodiment illustrated in FIG. 1 with additional parasitic arrays in the vertical plane, each pair of arrays acts with respect to the main array to increase the virtual aperture in the plane in which they lie. The parasitic arrays are positioned outside the field of the feed 13, which is placed in front of a reflector 12, as presented with respect to the two-dimensional embodiments. The change from a twodimensional to a three-dimensional array provides additional Wave channels fed by coupling from the center array, and adjustments for amplitude and a uniform phase front in the virtual aperture are achieved in the same manner as that defined relative to the two-dimensional arrays. Coupling of energy is increased by placing the parasitic arrays within the virtual aperture although, as noted relative to the embodiment of FIG. 1, parasitic arrays could be placed slightly outside the virtual aperture depending upon the amount of coupling desired. The addition of the parasitic arrays in the third dimension thus provides additional gain and pattern improvement with an attendant increase of the virtual aperture.

Thus, the performance of an endfire array may be explained relative to the concept of a virtual aperture located at the end of the array, and accomplishment of control of this aperture by coupling energy parasitic-ally from the main array into adjacent side rows.

Utilization of the teachings of my invention produce changes in side lobe level and gain, simultaneously. These accomplishments are obtained by low cost antenna construction without an appreciable increase in space compared with conventional endfire arrays of the same length. Furthermore, the initial feed system can be used without complicated power distribution networks common to other antenna capable of producing comparable results.-

Non-symmetrical arrangements of the parasitic arrays fall within the scope of my invention in that assymetry produces a change in the pattern of the resulting beam; therefore, it follows that a sweep for scatter propagation may be achieved by changing the phase by changing the height of the parasitic arrays; e.g., as shown in FIG. 4, by attaching the monopoles to a single support 26 and moving the elements through the ground plane and controlling the height by means of an eccentric or cam 27 acting on said support or by rotating the dipoles of the parasitic side rows which, in effect, change their electrical length.

Although the invention has been described with reference to particular embodiments, it will be understood to those skilled in the art that the invention is capable of a variety of alternative embodiments within the spirit and scope of the appended claims.

I claim:

1. A three-dimensional antenna array comprising a main center array being excited by a single feed and having a virtual aperture predetermined by the characteristics of said main array, a multiplicity of parasitic arrays, each of said arrays having energy coupled thereto exclusively by way of said main center array, at least one of said parasitic arrays being horizontally displaced from said main array and at least one other of said parasitic arrays being displaced vertically from said main array, said horizontally and vertically displaced arrays operating to modify said virtual aperture in the horizontal and vertical direction, respectively, to obtain increased gain by narrowing the beam pattern therefrom.

2. A three-dimensional antenna array comprising a main center array being excited by a single feed and having a virtual aperture predetermined by the characteristics of said main array, and a multiplicity of parasitic arrays, each of said parasitic arrays having energy coupled thereto exclusively by way of said main center array wherein said energy coupled thereto travels in the same longitudinal direction as that of said main center array, at least one of said parasitic arrays being horizontally displaced from said main center array to modify said virtual aperture in the horizontal direction, and at least one of said parasitic arrays being vertically displaced from said main outer array to modify said virtual aperture in the vertical direction.

3. A three-dimensional antenna array comprising a main center array being excited by a single feed and having a virtual aperture determined by the characteristics of said main array, four parasitic arrays, each of said arrays having energy coupled thereto exclusively by Way of said main array, said coupled energy traveling in the same longitudinal direction towards said virtual aperture as in said main array, two of said four parasitic arrays being positioned horizontally on either side of said main array, and the other two of said four parasitic arrays being positioned vertically on either side of said main array, wherein said vertically displaced parasitic arrays operates to modify said virtual aperture in the vertical direction and said horizontally disposed parasitic arrays operates to modify said vertical aperture in the horizontal direction.

4. A three-dimensional antenna array comprising a main center array being excited by a single feed and havin a beam pattern determined by the characteristics of said main center array, a multiplicity of parasitic arrays, each of said parasitic arrays having the longitudinal axis thereof in approximately parallel relationship to that of said main array and further being positioned at a predetermined distance therefrom to provide energy thereto exclusively by coupling from said main array, at least one of said parasitic arrays being horizontally displaced from said main array to modify said beam pattern to increase the gain, and at least one of said parastic arrays being vertically displaced from said main array to modify said beam pattern to further increase the gain.

References Cited by the Examiner UNITED STATES PATENTS 1,745,342 1/1930 Yagi 343-834 X 1,860,123 5/1932 Yagi 343-837 X 2,049,070 7/ 1946 Mathieu 343-837 2,415,807 2/1947 Barrow et al 343-786 X 2,624,003 12/1952 Iarns 343-785 X 2,663,797 12/1953 Kock 343-785 X 2,886,813 5/1959 Hings 343-819 3,096,520 7/1963 Ehrenspeck 343-819 X 3,159,839 12/1964 Hings 343-819 HERMAN KARL SAALBACH, Primary Examiner.

ELI LIEBERMAN, Examiner, 

1. A THREE-DIMENSIONAL ANTENNA ARRAY COMPRISING A MAIN CENTER ARRAY BEING EXCITED BY A SINGLE FEED AND HAVING A VIRTUAL APERTURE PREDETERMINED BY THE CHARACTERISTICS OF SAID MAIN ARRAY, A MULTIPLICITY OF PARASITIC ARRAYS, EACH OF SAID ARRAYS HAVING ENERGY COUPLED THERETO EXCLUSIVELY BY WAY OF SAID MAIN CENTER ARRAY, AT LEAST ONE OF SAID PARASITIC ARRAYS BEING HORIZONTALLY DISPLACED FROM SAID MAIN ARRAY AND AT LEAST ONE OTHER OF SAID PARASITIC ARRAYS BEING DISPLACED VERTICALLY FROM SAID MAIN ARRAY, SAID HORIZONTALLY AND VERTICALLY DISPLACED ARRAYS OPERATING TO MODIFY SAID VIRTUAL APERTURE IN THE HORIZONTAL AND VERTICAL DIRECTION, RESPECTIVELY, TO OBTAIN INCREASED GAIN BY NARROWING THE BEAM PATTERN THEREFROM. 